Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$35.47	3.818%	$36.8242	$36.82	$36.80	$36.80
Purchase #2	$55.84	3.142%	$57.5945	$57.59	$57.60	$57.60
Purchase #3	$103.79	13.712%	$118.0217	$118.02	$118.00	$118.00
Purchase #4	$137.85	4.772%	$144.4282	$144.43	$144.45	$144.40
Purchase #5	$170.38	12.301%	$191.3384	$191.34	$191.35	$191.30
Purchase #6	$187.67	8.658%	$203.9185	$203.92	$203.90	$203.90
Purchase #7	$112.50	9.775%	$123.4969	$123.50	$123.50	$123.50
7 purchase totals =	$803.50		$875.6224	$875.62	$875.60	$875.50